1. Field of the Invention
The present invention relates generally to the field of neutral pulse stimulation system and more particularly to control circuits directed to providing quantitative control of such systems.
More specifically, this invention relates to methods and apparatus for controlling the quantity of energy delivered to body tissue in a given time by accurately controlling the pulse dosage by means of digital control circuitry.
2. Description of the Prior Art
Devices and techniques for applying electrical pulse stimulation to various parts of the human body are, of course, well known. Over the recent past, these devices and techniques have been progressively refined, and specialized apparatus for various pulse stimulation procedures have appeared. As an illustrative example of a system directed specifically to stimulation of an area or areas of the nervous system such as the cerebellum, reference is made to a Dual Channel Cerebellar System (Physican's Information Manual .COPYRGT. published in 1976 by Medtronic, Inc.) which shows the use of a dual-channel apparatus having a two radio frequency capability for transmission of various stimulus pulses alternately to selected receptor sites such as the left anterior cerebellar cortex and the right anterior cerebellar cortex. Conventionally, the pulses are applied in a bipolar manner to alleviate deleterious effects which occur from unidirectional net current flows and are applied in alternate time intervals to minimize the fatigue of biochemical mechanisms such as depletion of neurotransmitter substances as synapic junctions. Additionally, very low power drain systems have evolved making it feasible to consider the implantation of counterpart receiving systems such that the stimulation procedure can be accomplished on successive occasions without unduly traumatizing the patient with repetitive electrode positioning.
An example of an implantable system for stimulation of body tissue is provided in U.S. Pat. No. 3,773,051 to Wade G. Holcomb et al. Holcomb teaches the use of an RF link to deliver pulses of prescribed amplitudes to body tissue wherein a single channel transmitter is used to transmit pulses of controlled durations to an implanted receiver which converts the transmitteed duration information into amplitude information prior to applying the stimulation in the form of pulses to the electrode site. The technique disclosed is particularly effective in assuring the transmission of controllable amplitude pulses despite the vagaries of the radio frequency (illustratively 300 Khz-3Mhz--i.e., MF to HF range) propagation path.
U.S. Pat. No. 3,888,261 to Donald D. Mauer, and assigned to the same assignee of the present application, teaches the techniques of using a pair of transmission channels to transmit pulse trains in a time-shared sequence to alternate receptor sites. The two-channel technique disclosed is well suited for carrying independent stimulus pulse trains to the separate sites and is exploited by having each time-shared channel adapted to carry pulse trains of independently controllable amplitude. Also of interest in Maurer is the use of a pair of distinct frequencies in the RF link such that the independent pulse trains generated are assured of being unambiguously carried in isolated channels to their intended receptor site.
While the available devices and techniques represent useful solutions to a number of difficulties associated with administering pulse stimulation to highly sensitive portions of human body tissue, none have addressed a key aspect of pulse stimulation--that of administering precise pulse dosages. The present invention is directed to providing a useful solution of this specific problem area.